1. Related Technical Fields
Related technical fields include systems, methods, and programs, capable of identifying a route traveled by a vehicle.
2. Description of the Related Art
Nowadays, many vehicles are equipped with a navigation apparatus that provides route guidance so that a driver can easily reach a destination. A typical navigation apparatus detects a current vehicle position using a GPS receiver, acquires map data corresponding to the current position from a storage medium such as a DVD-ROM or an HDD or via a network, and displays the map on a liquid crystal display monitor. If a user specifies a destination, the navigation apparatus searches for a route from the vehicle position to the specified destination and displays a recommended route on a display screen. When the vehicle is approaching each intersection, voice guidance is provided so that the driver can reach the destination.
When a route is searched for, various “costs” are defined for links or nodes depending on, for example, road types such as expressways, toll roads, national roads, major local roads, prefectural roads, minor streets, etc., traffic restrictions such as a turn restriction, a one-way restriction, etc., link lengths, road widths, the number of traffic lanes, etc. The “cost” is generally a measure of the desirability of including an associated link or node in a recommended route. To search for an optimum route from a current vehicle position to a destination, links described in map data are examined starting from both the current vehicle position and the destination to find an optimum route. When a route found in searching started from the current vehicle position meets somewhere a route found in searching started from the destination, the sum of costs for the route from the current vehicle position and the sum of costs for the route from the destination are added together to determine the total cost. The total cost is calculated for each possible route, and a route having a minimum total cost is employed as a navigation route.
A travel time needed to travel each link is one of factors that may be considered in determining the cost during route searching. However, the travel time depends not only on the link length and the link type but also other traffic conditions such as congestion. Thus, real-time traffic information (in terms of congestion etc.) is needed to predict the travel time. It is known to collect such traffic information using sensors installed on roadsides, as is the case in Vehicle Information and Communication System (VICS®). It is also known to collect traffic information from particular vehicles called information probing vehicles running on roads.
For example, Japanese Unexamined Patent Application Publication No. 2003-281674 discloses a traffic information processing system adapted to determine point-to-point travel times and determine whether there is traffic congestion, on the basis of times at which information probing vehicles pass through two specified points.